1. Field of the Invention
The present invention relates generally to a device and method for processing an image, and in particular, to a preprocessing device and method for recognizing characters included in an image.
2. Description of the Related Art
Typically, a preprocessing operation is performed in order to recognize image characters. “Preprocessing operation” refers to an operation of processing an image prior to recognition of characters in the image. The image preprocessing operation can include determining whether an input image is appropriate for character recognition, correcting a skew of an object in an input image, properly correcting a size of an input image, and binarizing an input image so that characters in the input image can be recognized.
First, an image received for preprocessing can be an image photographed with a camera. When an object is unfocused or irregularly illuminated during photographing, the photographed image may become blurred. Recognizing characters in such a blurred image reduces the recognition rate. Therefore, it is preferable to determine whether an input image is blurred, prior to recognizing characters in the image. If resolution of the image is too low to recognize characters therein, it is preferable to interrupt a recognition operation and then request a re-input of the image.
Second, a device for recognizing image characters generally recognizes characters included in an image. Because the image is photographed by a camera, an object in the image may be skewed. Therefore, in order to increase the recognition rate, it is preferable to correct a skewed object in the image prior to performing a recognition operation.
Third, a device for recognizing image characters generally recognizes characters from an image. The image is divided into a character region and a background region, and no character is arranged in the background region. For example, assuming that a document subject to character recognition is a business card, an input image becomes an image of the business card. The input image includes a background region outside the business card. In this case, it is possible to improve character recognition performance by extending a size of the image after removing the background region from the image. In addition, typically, a character region is not included in the edges of the business card. Therefore, it is possible to improve recognition performance by searching for a position of a character region in a business card, removing regions other than the character region according to the search results, and then extending the character region by a percentage of the removed regions. Storing such preprocessed image contributes to an increase in memory efficiency.
Fourth, an image is binarized prior to characters in the image being recognized. However, when binarization is performed on the entire photographed image in an irregularly lighted situation, with a shadow thrown thereon, the binarization performance is undesirably deteriorated. In order to improve the binarization performance, it is preferable to classify the image into blocks having a predetermined size and then independently binarize the classified image blocks.